Our previous work (Biochem. Biophys. Acta. 338: 43,1974), and theoretical considerations indicated that the alteration by carcinogens in the rate of degradation of certain proteins of cytoplasmic structures is an important factor in the mechanism of chemical carcinogenesis. It is planned to extend this investigation to the study of changes produced by chemical carcinogens in the degradation rates (half-lives) of various fractions of the nuclear acidic proteins from rat liver, during hepatocarcinogenesis and from developed primary and transplantable hepatomas.